相关论文: Large-scale surveys of the quasar proximity effect
We present measurements of the ionising ultraviolet background (UVB) at z ~ 5-6 using the quasar proximity effect. The fifteen quasars in our sample cover the range 4.6 < z_q < 6.4, enabling the first proximity effect measurements of the…
We examine the local density environments around 67 quasars at $z\sim3$, by combining the imaging data of Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) and Canada-France-Hawaii Telescope Large Area U-band Survey (CLAUDS) over about…
We measure the large-scale cross-correlation of quasars with the Lyman \alpha\ forest absorption in redshift space, using ~ 60000 quasar spectra from Data Release 9 (DR9) of the Baryon Oscillation Spectroscopic Survey (BOSS). The…
We present the first results from our survey of intervening and proximate Lyman limit systems (LLSs) at $z$$\sim$2.0-2.5 using the Wide Field Camera 3 on-board the Hubble Space Telescope. The quasars in our sample are projected pairs with…
We investigate the luminosity and redshift dependence of the quasar continuum by means of composite spectrum using a large non-BAL radio-quiet quasar sample drawn from the Sloan Digital Sky Survey. Quasar continuum slopes in the UV-Opt band…
We study the dependence of the number density and properties of quasars on the background galaxy density using the currently largest spectroscopic datasets of quasars and galaxies. We construct a galaxy number density field smoothed over…
The composite spectra of quasars are widely used as templates for redshift determination, as well as for measurements of the mean transmission in Ly\alpha-forest studies, and for investigation of general spectral properties of quasars.…
The intense radiation emitted by luminous quasars dramatically alters the ionization state of their surrounding IGM. This so-called proximity effect extends out to tens of Mpc, and manifests as large coherent regions of enhanced…
The matter density field at $z\sim 6$ is very challenging to probe. One of the traditional probes of the low density IGM that works successfully at lower redshifts is the Lyman-alpha forest in quasar spectra. However, at the end of…
Using the Sloan Digital Sky Survey, Data Release 5, we survey proximate damped Lya systems (PDLAs): absorption line systems with HI column density N(HI)> 2x10^20 cm^{-2} at velocity separation dv < 3000 km/s from their background quasar.…
The distribution of neutral hydrogen in the intergalactic medium (IGM) is currently explored at low-z by means of UV spectroscopy of quasars. We propose an alternative approach based on UV colours of quasars as observed from GALEX surveys.…
In merger-driven models of massive galaxy evolution, the luminous quasar phase is expected to be accompanied by vigorous star formation in quasar host galaxies. In this paper, we use high column density Damped Lyman Alpha (DLA) systems…
The Dark Energy Spectroscopic Instrument (DESI) will measure millions of quasar spectra by the end of its 5 year survey. Quasar redshift errors impact the shape of the Lyman-$\alpha$ forest correlation functions, which can affect…
The recent compilation of quasar (QSO) X-ray and UV flux measurements include QSOs that appear to not be standardizable via the X-ray luminosity and UV luminosity ($L_X-L_{UV}$) relation and so should not be used to constrain cosmological…
Cosmic photons can be efficiently collected by broadband intensity mapping but information on their emission redshift and frequency is largely lost. We introduce a technique to statistically recover these otherwise collapsed dimensions by…
We revisit the proximity effect produced by QSOs at redshifts 2.1-3.3 applying the FLO approach (Saitta et al. 2008) to a sample of ~6300 Ly-alpha lines fitted in 21 high resolution, high signal-to-noise spectra. This new technique allows…
We present the results from the optical component of a survey for damped Lyman-alpha systems (DLAs) towards radio-loud quasars. Our quasar sample is drawn from the Texas radio survey with the following primary selection criteria: z_em >…
The Photometric objects Around Cosmic webs (PAC) approach developed in Xu et al. (2022b) has the advantage of making full use of spectroscopic and deeper photometric surveys. With the merits of PAC, the excess surface density…
We study the density field around z_em > 4 quasars using high quality medium spectral resolution ESI-Keck spectra (R~4300, SNR > 25) of 45 high-redshift quasars selected from a total of 95 spectra. This large sample considerably increases…
The impact of quasars on their galaxy neighbors is an important factor in the understanding of the galaxy evolution models. The aim of this work is to characterize the close environments of quasars at low redshift (z$<$0.2) with the most…